Perfluorocarbon based polymeric coatings having low critical surface tensions

ABSTRACT

Polymers comprising pendant rearranged oxazoline and/or oxazine portions linked to a perfluorocarbon moiety having a perfluoroalkyl group are prepared. Such polymers can provide coating compositions which exhibit critical surface tensions of wetting of less than about 15 dynes/cm.

BACKGROUND OF THE INVENTION

This invention relates to novel perfluorocarbon based polymericmaterials useful as release coatings and to processes for using suchcoatings as mold release agents.

A wide variety of molding applications require molding apparatus withsurfaces which will easily release molded articles and moldingmaterials. Polymer deposits on molding apparatus surfaces resulting fromthe "sticking" occurring during molding processes not only make it moredifficult and time consuming to remove molded parts from said molds, butsuch deposits have a tendency to deteriorate and fragment, thusdecreasing the quality of the surfaces of products molded therefrom.

One approach directed towards obtaining surfaces which readily releaseadhesives has involved the application of various hydrocarbon andsilicone oils and waxes to the surfaces of molds which are exposed tosaid polymer compositions. Commonly, hydrocarbon and silicone oils andwaxes are sprayed or wiped onto injection molding apparatus, which isthen used for the molding of polymers and prepolymers. Unfortunately, itis generally the case that only one to about three injection cycles maybe performed before it is necessary to retreat the mold with saidnonstick agents.

Another approach for providing molding apparatus surfaces which havegood release characteristics is the application of fluorinated polymers,such as tetrafluoroethylene. These types of polymers are typicallyapplied to a surface as small solid particles or as a coating.Unfortunately, these types of polymers are typically bound to surfaceswith nonfluorinated binders or by a difficult process involvingsintering of the polymer particles at high temperatures.

Perfluorinated polymers are believed to release because they produce avery low critical surface tension of wetting (γ_(c)). More recently, asdisclosed in U.S. Pat. No. 4,344,993, a combination of a hydrophilicpolymer with up to about 0.5 weight percent perfluorocarbon andcrosslinked with a cyclic sulfonium zwitterion yields a surface coatinghaving a surface tension of wetting of less than that of coatingsconsisting of 100 percent perfluorocarbon. Although this type of coatingis useful for preventing deposits of nonaqueous polymerization reactantsand products from adhering to reactor surfaces in the production ofolefinic polymers, such a coating does not adhere adequately to surfacesof conventional molding apparatus when amounts of perfluorocarbongreater than 0.5 weight percent are employed.

Therefore, it is highly desirable to provide an improved coating whichadheres well to a molding apparatus surface, and a process for usingsame which will significantly reduce the undesirable deposition ofmaterial and sticking on internal surfaces of molding apparatus byproviding a low γ_(c).

SUMMARY OF THE INVENTION

The present invention is a polymer comprising pendant rearrangedoxazoline and/or oxazine portions linked to a perfluorocarbon moietyhaving a perfluoroalkyl group.

In another aspect, the present invention is an adherent coatingcomposition comprising the polymer of this invention.

The amount of perfluorocarbon moiety present in the polymer is such thatthe resulting coating can exhibit a critical surface tension of wettingof less than about 15 dynes per centimeter (dynes/cm). Surprisingly, theperfluorocarbon-containing polymer coating composition of the presentinvention can provide a surface having a critical surface tension lessthan that of a coating consisting entirely of a linear perfluorocarbon,such as a homopolymer of tetrafluoroethylene. The coating composition ofthis invention provides a permanently bound coating which can be easilyapplied, and which is not removed or wet by most solvents.

In another aspect, the present invention is a composition comprising apolyisopropenyl-2-oxazine and/or polyisopropenyl-2-oxazoline containingpolymer, a nucleophilic fluoroalkyl-containing carboxylic acid, and asuitable solvent. When cured, said composition yields the aforementionedadherent coating composition, as defined hereinbefore. In yet anotheraspect, this invention is a coated substrate wherein said composition iscontacted with the substrate and cured.

The coating compositions of this invention are particularly useful inreducing the amount of sticking of material on the internal surfaces ofthe molding apparatus. Accordingly, in another aspect, this invention issuch a process for reducing the sticking of material to surfaces such asinternal surfaces of molding apparatus which comprises applying asolution of the aforementioned composition to the internal surfaces ofmolding apparatus and curing. Such a process is advantageously employedin the molding of polymers such as polyethylenes, polypropylenes,polycarbonates, polyurethanes, and the like.

DETAILED DESCRIPTION OF THE INVENTION

The 2-alkenyloxazoline or 2-alkenyloxazines of the present inventionhave the general formula: ##STR1## wherein A is hydrogen or lower alkyl,preferably methyl; and each of R² is independently hydrogen, alkyl,aralkyl, hydroxyalkyl, phenyl or inertly substituted phenyl, such thatthe reactivity of the monomer is not significantly diminished, asrequired herein; preferably each of R² is hydrogen; and n is 0 or 1.Examples of suitable 2-alkenyloxazolines (i.e., oxazoline monomers) and2-alkenyloxazines (i.e., oxazine monomers), and their methods ofpreparation are catalogued in U.S. Pat. Nos. 3,505,297 and 4,144,211,which are incorporated herein by reference. Examples of preferred2-alkenyloxazolines include 2-isopropenyloxazoline, 2-vinyloxazoline,and 5-methyl-2-isopropenyloxazoline.

Polymers of this invention are generally represented by the formula:##STR2## wherein a+b+c+d=1, a is greater than 0, b is from about 0 toabout 0.9, c is from about 0 to about 0.9, d is from 0 to about 0.8, andm is preferably about 100 to about 10,000. A is H or methyl. Y¹ is asdefined hereinafter. R¹ is the remaining portion of the oxazoline oroxazine moiety and can be described as disclosed hereinbefore. R_(F) issaturated perfluoroaliphatic containing moiety as described hereinafter.X can vary and is preferably an essentially nonionic moiety or an ionicmoiety. X can include, for example, a moiety derived from butadiene,isoprene, ##STR3## wherein R is hydrogen or alkyl comprising from 1 toabout 12 carbon atoms or a carboxy functionality. Y is the remainingportion of a polycarboxylic acid or other species containing an acidichydrogen and is present in such a way that crosslinking is introduced tothe polymer system. R_(A) is an alkyl or aryl moiety as definedhereinafter.

Polymers of this invention are advantageously prepared by reacting2-alkenyloxazoline and/or 2-alkenyloxazine monomers and optionally othermonomers in order to obtain a polymer comprising pendant 2-oxazoline or2-oxazine functionalities. The polymer is contacted with aperfluoroalkyl-containing acid and optionally, the other acids asdefined hereinafter. The mixture is then subjected to conditions suchthat the acid functionality reacts with an oxazoline or oxazinefunctionality to form an amide-ester linkage.

Crosslinking can be introduced to the polymer with a polyfunctionalnucleophilic species such as carboxylic acid. Low equivalent weightpolyfunctional carboxylic acids are preferred. Preferred polyfunctionalcarboxylic acids are the di- and tri-carboxylic acids. Examples ofdi-carboxylic acids include those represented by the formula: ##STR4##where t can range from 1 to about 40. The amount of crosslinking canvary and is employed in order to form a harder, more rigid product.Other suitable polyfunctional nucleophilic species include thepolymercaptans, phenols, protonated amines, aromatic carboxylic acidssuch as terephthalic acid, unsaturated carboxylic acids, and the like.

Moieties designated as R_(A) generally are any alkyl or aryl moietieshaving functionalities which can be reacted with a pendant oxazoline oroxazine moiety to yield a pendant grouping as described hereinbefore.For example, R_(A) can be derived from a carboxylic acid having fromabout 4 to about 25 carbon atoms. R_(A) can also be derived from alkylsulfonates, alkylphosphonates, and the like.

Perfluoroalkyl-containing acids suitably employed in the practice ofthis invention include organic compounds represented by the formula:

    R.sub.F --Y.sup.1 --COOH

wherein R_(F) is a perfluorocarbon or a saturated perfluoroaliphaticmoiety containing a F₃ C⁻ moiety and is linked to the carboxylic acidmoiety through a moiety which does not substantially interfere with thenucleophilicity of the carboxy group, (i.e., Y¹) advantageously ahydrocarbon moiety preferably containing at least 2 carbon atoms. Ifdesired, the perfluoroaliphatic moiety containing a F₃ C⁻ moiety can belinked to a group such as a sulfonate, phosphonate, and the like,through a group such as Y¹. The perfluoroaliphatic or perfluorocarbonmoiety advantageously contains from about 3 to about 18 carbons whereinsubstantially all are fully fluorinated, preferably from about 3 toabout 14, more preferably from about 3 to about 10 of such carbonssubject to the limitation that the fluoroaliphatic moiety is linked tothe carboxylic acid moiety through an aliphatic hydrocarbon moiety(i.e., Y¹) containing at least 2 carbon atoms. R_(F) can be linear,branched or cyclic, preferably linear. Y¹ contains a carbon-bondedhydrogen and can contain an oxygen atom, sulfur atom and/or a nitrogenatom bonded only to carbon atoms in the skeletal chain. More preferableare those linear perfluoroaliphatic moieties (i.e., R_(F)) representedby the formula: C_(n) F_(2n+1) wherein n is the range of about 3 toabout 10. Most preferred are those linear perfluoroaliphatic moietiesrepresented in the paragraph below.

Prefluorocarbon containing carboxylic acids of the formula CF₃ (CF₂)_(p)SO₂ NH(CH₂)_(q) COOH; wherein p is from about 2 to about 15, preferablyabout 2 to about 9, and q is from about 2 to about 4 are preferred. Anespecially preferred perfluorocarbon containing carboxylic acid is thecarboxylic acid form of the perfluorocarbon sold by DuPont under thetrade name Zonyl® FSA; or the carboxylic acid form of theperfluorocarbon sold under the trade name Fluorad® FC 129 by the 3MCorporation. Examples of other preferred anionic perfluorocarbonstarting materials, as well as methods of preparation, are illustratedin U.S. Pat. Nos. 3,172,910 and 3,630,951.

The polymer containing pendant oxazine or oxazoline moieties are thenadvantageously contacted with a nucleophilic fluoroalkyl-containingcarboxylic acid in the presence of a liquid that is a solvent for eachof the species (i.e., a suitable solvent). Typically, such solventsinclude the alkanols such as ethanol, propanol, butanol, glycols,mixtures of suitable alkanols and mixtures of the alkanols with water.The polymer containing pendant oxazine or oxazoline moieties can beemployed in the form of a dispersion in an aqueous medium, as taught inU.S. Patent Application Ser. Nos. 504,119 and 504,120; each filed June14, 1983, now issued U.S. Pat. Nos. 4,474,923 and 4,508,869respectively; and which are incorporated herein by reference. Ifdesired, aqueous ammonia can be added to the formulation in order toincrease shelf life of the mixture. In particular, the pendant oxazolineor oxazine moiety undergoes a rearrangement in the presence of thefluoroalkyl-containing acid to produce an amide-ester linkage. Thisreaction is initiated, for example, by heat and/or loss of solvent (orliquid phase) after the polymer, fluoroalkyl-containing acid and solvent(or liquid phase) are applied to the surface of the substrate which isbeing treated.

Accordingly, the coating composition can be applied directly (i.e.,without the prior application of a primer coating) to the interiorsurfaces of the molding apparatus in a convenient manner, such aswiping, spraying, brushing on, and the like. Brushing has been found tobe satisfactory since it ensures complete coverage of all surfaces. Anyuncovered areas, such as pinholes, etc., should be avoided since suchexposed areas provide sticking sites for polymer build-up. It is mostdesirable that one layer of coating be applied. The amount of coatingapplied for the thickness thereof is not particularly critical so longas a continuous film over all interior surfaces of the molding apparatusis provided. In some instances, it is preferable to pretreat theinternal surfaces of the reaction vessel with conventional chemicalcoupling agents. For example, prehydrolyzed silane coupling agents suchas ##STR5## and the like are particularly useful for this purpose.

When said coating compositions are applied to the surface of a moldingapparatus and cured, the resulting coatings are (1) inert to anypolymeric reagents which will contact the coating in subsequent use, (2)can have a γ_(c) of less than about 15 dynes/cm, and (3) will not wetwith any common solvents.

Following the application of the coating composition of the interiorsurfaces of the mold, including product transfer conduits, etc., thecoating can be heated in order to dry and cure the same. Any suitableheating method can be employed, such as radiant heating, heated air, andthe like. Usually, temperatures within the range of 90° to about 160° C.are sufficient; with temperatures in the range of 110° to 160° C. beingpreferred. The temperature chosen will depend upon the time of drying.Thereafter, the molding to be carried out in the equipment can becommenced immediately. No particular modifications of processingtechniques are required due to the presence of the coating. Further,utilization of the internally coated mold of the present invention doesnot adversely affect the heat stability or other physical and chemicalproperties of the polymers or other molded products produced therein.Ordinary care should, of course, be exercised to avoid abrading orrupturing the coating.

Compositions of this invention can be applied to fabrics such as cottonand nylon. For example, compositions of this invention are useful intreating fabrics in order to provide water and/or oil resistance to thefabric. See, for example, U.S. Pat. Nos. 4,325,857 and 4,388,372.

The following examples are illustrative embodiments of this inventionand should not be construed as limiting its scope. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

A. A solution of 675 grams (g) water, 0.75 g sodium bicarbonate, 1.5 gsodium persulfate and 71.1 g of 2-isopropenyl-2-oxazoline is heated at50° C. under nitrogen in a 1-liter stirred flask. After 24 hours, 0.5 gof sodium persulfate in 100 milliliter (ml) of water is added andstirred for 1 hour. The resulting polymer has a molecular weight ofabout 300,000.

B. A coating solution is prepared by mixing 1.0 g of a 10 percentpolymer is diethylene glycol methyl ether (0.90 meq. active oxazoline)with 1.10 of a 0.80 meq./g solution of CF₃ (--CF₂)_(x) --CH₂ CH₂ SCH₂CH₂ COOH-- (x=3 to 18), (0.88 meq. of acid) in alkanol. To the resultingsolution, 1 g of alkanol and 0.3 g water are added. The resultingsolution is cast on a microscope slide and cured at 150° C. for 30minutes. The soft coating has a critical surface tension of wetting ofabout 10 dynes/cm. Nylon fabric is wet with the coating solution andcured at 110° C. for 1 hour. The resulting fabric will not wet witheither hexane or water.

C. A coating solution is prepared by mixing 1.0 g of a 10 percentpolymer in alkanol (0.90 meq. oxazoline) with 0.1 g of a 2.0 normalwater solution (0.20 meq. acid) of malonic acid and 0.8 g of a 0.80meq./g solution of CF₃ (CF₂)_(x) --CH₂ CH₂ SCH₂ CH₂ COOH(x=3 to 18),(0.65 meg. of acid) in alkanol. To the resulting solution 0.5 g alkanolis added. The coating solution is cast and cured at 150° C. for 30minutes. The coating has a pencil hardness of 2H and a critical surfacetension of wetting of about 12 dynes/cm.

What is claimed is:
 1. A polymer composition comprising pendantrearranged oxazoline and/or oxizane portions linked through anamide-ester linkage to a perfluorocarbon moiety having a perfluoroalkylgroup and having a recurring unit of the formula: ##STR6## wherein, A ishydrogen or methyl, R_(F) is a saturated perfluoroaliphatic moiety, Y¹is a hydrocarbon moiety containing at least 2 carbon atoms, and R¹ isthe remaining portion of a rearranged oxazoline or oxazine moiety.
 2. Acomposition of claim 1 represented by the formula: ##STR7## whereina+b+c+d=1, a is greater than 0, b is from about 0 to about 0.9, c isfrom about 0 to about 0.9, d is from about 0 to 0.8, m is from about 100to about 10,000, X is an essentially nonionic or ionic moiety and Y isthe remaining portion of a polycarboxylic acid and is present in such away that crosslinking is introduced to the polymer system, and R_(A) isan alkyl or aryl moiety.
 3. A composition of claim 2 wherein b=0, c=0and d=0.
 4. A composition of claim 2 wherein b=0 and d=0.
 5. Acomposition of claim 1 having repeating units of the formula: ##STR8##wherein A is hydrogen or methyl, and x is from about 3 to about
 18. 6.An adherent composition comprising the polymer of claim
 1. 7. Anadherent composition comprising the polymer of claim
 2. 8. A compositionof claim 1 wherein R¹ is ##STR9## where n is 0 or 1, and each of R² isindependently hydrogen, alkyl, aralkyl, hydroxyalkyl, phenyl or inertlysubstituted phenyl.
 9. A composition of claim 8 wherein each of R² ishydrogen.